The present disclosure relates to a laser scanning unit which includes a scanning lens that causes a light beam to form an image on a surface-to-be-scanned, and an image forming apparatus using the laser scanning unit.
A general laser scanning unit used in, for example, a laser printer, a copying machine, and the like includes a light source emitting a laser beam, a deflection member that deflects the laser beam and causes the laser beam to scan a surface-to-be-scanned, and a scanning lens that causes the deflected laser beam to form an image on a circumferential surface (surface-to-be-scanned) of a photosensitive drum. The scanning lens has a correction function that causes the laser beam to scan the surface-to-be-scanned at a constant speed.
In the laser scanning lens, it is important to scan the surface-to-be-scanned with a uniform amount of light in a main scanning direction. The scanning not performed with a uniform amount of light may result in degradation in uniformity of image density. One of factors that inhibit the scanning with a uniform amount of light is aberration of the scanning lens. A plurality of scanning lenses may be disposed in a laser scanning unit, or a laser scanning unit may be composed of a single scanning lens for the purpose of reduction in the size, cost, or the like of the unit. In the latter case, the degree of freedom in lens design is reduced, and aberration is likely to occur at a specific image height.